1. Field of the Invention
The present invention generally relates to improvements in stringed musical instruments and more particularly the replacement of the bass-bar which is traditionally installed on the underside of the top-plate of a cello or double bass and substituting a more elastic suspension system of radiating bars. In one arrangement, the bass-bar is replaced by a short support-bar located under the bass-foot of the bridge and has an arch cut at its midpoint in alignment with the bridge and a set of four fan-braces radiate outward at an angle to the alignment axis of the support-bar and are firmly glued to the sides of the support-bar with the fan-braces distributing the static load borne by the support-bar over the whole area of the top-plate. In another arrangement, the traditional bass-bar is replaced by a pair of tapered vibration-bars which cross in an integrally glued cross-lap joint with the region of crossing being provided with a slight arch-cut profile with the load from the X-brace region thus being spread over the entire top-plate of the instrument.
2. Description of the Prior Art
In the violin family of instruments, aside from all other similarities of form and construction and differences of dimension and shape, there are two crucial acoustical or vibrational elements in common: the sound-post, and the bass-bar.
The sound-post is a dowel of wood wedged between the top-plate and the back, and is located near (but not under) the treble-foot of the bridge. Apparently, this member has its origins in antiquity, and originally had a structural-support function, as it appears to have been disposed symmetrically near the bridge, supporting thin instrument tops against collapse under strong tension applied to the bridge.
In the violin family it was discovered that by setting the post with special tongs or forceps near the treble-foot of the bridge, but somewhat behind it toward the string tail-piece, the most brilliant treble tones would ensue. Location of the sound-post is thus a critical adjustment on the part of the luthier.
It is commonly said that the purpose of the sound-post is to transmit vibrations of the top-plate to the back-plate of the instrument (allegedly for sound enhancement). This is a false appraisal, and if it had been correct, a more efficient placement of the sound-post could be considered to be directly under the treble-foot of the bridge--a location which kills upper register response. Giltay, a Dutch engineer-physicist who did extensive research on violins, proved experimentally that the sound-post creates a null-point or node for high-frequency top-plate vibration. This is exactly analogous to playing harmonics on a string by tapping with the finger a nodal point on a string. Thus, a high frequency, small circular zone is created, with the treble-foot at a maximum (antinode) of vibration, and the sound-post at a node or null-point vibration. This is a local top-plate tuning-in of high frequency plate modes. No modification of sound-post structure is contemplated in this invention.
A century before Stradivari the efficacy of a "bass bar" was accidentally discovered by Gasparo da Salo. He found that a ridge of wood centered under the bass-foot of the bridge and extending the full length of the underside of the top-plate greatly enhanced the bass response of a violin. Stradivari glued in a spruce bass bar instead of carving a ridge of wood in the underside of the top-plate. This made it possible to replace the bass bar and to modify it. As steel strings replaced gut, and string tension and bridge pressure rose, the violin bass bar of today became twice as high as that of Stradivari's time. In applying the bass bar to the viola, cello and string bass, progressively sturdier bass bars were introduced, until a veritable fence-picket appears as the bass bar in the cello and string bass (bass viol).
The virtuoso musician perceives an increasing deficiency in low-register tones as one goes up the series violin-viola-cello-bass: the low fundamental is missing or quenched in the bass register. The result is progressively a "drier" or more nasal tone, with upper partials dominating.
If we study the desired function of the bass bar and its actual action, we can diagnose the source of its deficiency. Without a bass bar the bass-foot of the bridge would drive local vibrations of the top-plate, emphasizing the high harmonics of the string vibration. A bass bar is then introduced to couple the local bridge motion over an extended region of the top-plate, so that low-frequency components of the string vibration could be coupled.
The contradiction then exists that the bass bar is highest and therefore stiffest just at the point (under the bass-foot of the bridge) where the amplitude of motion should be greatest.
For the violin and viola, I previously introduced arch-cuts in the bass bar centered under the bass-foot of the bridge. This arch-cut then permits flexing of the bass bar at its center, but still supporting string tension, and now more efficiently coupling bridge motion to full top-plate motion. The result was that for violins, and especially for violas, unplayable student instruments became fairly decent, and the low register was much enriched, especially in the viola. Long-term tests under full string tension showed no perceptible top failure. An unexpected dividend was the improvement of the overall range of the instrument, especially the treble. The arched bass bar evidently does function to strengthen fundamental components of each note.
For the string-bass (bass viol) and also cello, because of their much greater dimension, another engineering physics design element is introduced here. A mere arch-cut in the heavy bass bar of these instruments would do little to reduce the mass and general stiffening effected by those heavy bars. My fan-bracing design uses a short, arched support-bar which imparts some flexibility and a greatly reduced mass. This short bar should result in a more rapid action of greater amplitude. The principal change is in the introduction of fan-bracing as highly flexible coupling-bars attached to the short support-bar. The overall effect should be a coupling array which facilitates high-amplitude bass-register vibrations to be spread over the full length of the top-plate. The true bass fundamental should then be reinforced.
A Belgian engineer-physicist who studied violin mechano-acoustics states that the violin design problem is one which no engineer has faced: a highly flexible, dynamic design (for good sound production) simultaneously with a very stiff, static characteristic (for support of high string tension and consequent bridge force load). I believe that the fan-bracing design introduced permits the sustaining of a high bridge load and at the same time permits greatly improved low-frequency response by a more responsive all-top-plate motion.
I have also introduced an X-bracing system to replace the traditional bass-bar in a cello and double bass in which a pair of tapered vibration bars cross in an integrally glued cross lap joint which supports the static load with the load from the X-brace region being spread over the entire top-plate which also is believed to permit greatly improved low frequency response by a more responsive all top-plate motion.